1. Technical Field
The present invention relates to a liquid ejection head having a piezoelectric element and a liquid ejection apparatus.
2. Related Art
Examples of a liquid ejection head include an ink jet printhead having a piezoelectric element made up of first electrode, a piezoelectric layer, and a second electrode on one side of a flow-channel-containing substrate having pressure generating chambers which communicate with nozzle openings, and configured to cause a pressure change in the pressure generating chambers by driving the piezoelectric element and discharge ink drops from the nozzle openings. The piezoelectric element employed in the ink jet printhead has a problem of being susceptible to damage due to an external environment such as humidity. In order to solve this problem, for example, there is a piezoelectric element covered with a second electrode on an outer surface of the piezoelectric layer (see JP-A-2005-88441, for example). In JP-A-2005-88441, the first electrode is a common electrode, and the second electrode is individual electrode.
There is also proposed a configuration in which the first electrodes of the piezoelectric element are provided for the respective pressure generating chambers as the individual electrodes, and the second electrode is provided across the plurality of pressure generating chambers continuously as the common electrode (see JP-A-2009-172878, FIG. 2 and FIG. 4, for example).
However, in the piezoelectric element in which the second electrode is employed as the common electrode as shown in FIG. 2 and FIG. 4 in JP-A-2009-172878, an end of the second electrode in the longitudinal direction of the pressure generating chamber is disposed in an area opposing the pressure generating chamber. Therefore, there arises a difference in rigidity between an area where the second electrode is disposed and an area where the second electrode is not disposed. Simultaneously, since the area where the second electrode is disposed and the area where the second electrode is not disposed define an boundary between an area where an electric field is generated (active portion) and an area where the electric field is not generated (non-active portion), a stress concentration occurs at the boundary between the active portion and the non-active portion, which leads to a probability of occurrence of destruction such as cracks in the piezoelectric layer.
The problem as described above exists not only in the ink jet printhead, but also in the liquid ejection head which ejects liquid other than ink.